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QEV Bolt-action cannon design help

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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QEV Bolt-action cannon design help

Unread postAuthor: Ed » Thu Aug 02, 2012 5:52 pm

Hi, I'm new here at spudfiles, and this is my first post. I've been looking to make my own spudgun for some time now, and since I'm located in CA, I'm restricted to making pneumatic spudguns.

I'm planning to make an over/under style pneumatic handheld spud gun with some form of a bolt-action mechanism, interchangeable barrels and a 3/4" QEV valve. Unfortunately, I'm not so familiar with spudding and would like some help from you guys regarding design, construction, and components.

-Regarding design, I'm not sure how a QEV valve works when in use inside a launcher, and how it affects a launcher's overall design.
-The bolt action mechanism I have planned is basically a bolt sliding back and forth in the breech that pushes projectiles into the barrel, but I don't know how to make it airtight or adapt to different barrel diameters.
-The barrel will probably be around 4' long, so you have a sense of the planned size.
-I'm not looking to use any electronics in this design.

-On components, I'm leaning towards pvc, but depending on the average cost and weight of a metal launcher around the same size, I might turn to metal.
-I'll also need advice on the various valves, hoses, and parts that I'll use.
-For example, I'll hook up the launcher to an air compressor or a co2 tank, depending where I am. What valve should I use?

As I refine the design and finalize the list of components I'll ask for tips and methods on the various inevitable mods that pop up during construction.

Thanks for taking your time to read this.

Ed
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Re: QEV Bolt-action cannon design help

Unread postAuthor: jackssmirkingrevenge » Thu Aug 02, 2012 10:09 pm

Ed wrote:-Regarding design, I'm not sure how a QEV valve works when in use inside a launcher, and how it affects a launcher's overall design.


Here's a typical QEV launcher:

Image

A QEV typically has three ports:

Image

1 is where you attach you pilot valve, the valve you open to fire the thing. In the example above, it's a blowgun. The filling valve is also typically attached here.

2 is where your air chamber goes.

3 is where your barrel goes.

-The bolt action mechanism I have planned is basically a bolt sliding back and forth in the breech that pushes projectiles into the barrel, but I don't know how to make it airtight or adapt to different barrel diameters.


Another alternative would be to make a hole in the barrel covered with a sleeve, something likethis golf ball launcher:

Image

Image

-The barrel will probably be around 4' long, so you have a sense of the planned size.


What calibre/s are you planning on, and what performance do you expect?

-I'm not looking to use any electronics in this design.


Not needed for a QEV launcher.

-On components, I'm leaning towards pvc, but depending on the average cost and weight of a metal launcher around the same size, I might turn to metal.


For small bores, higher pressure is a must, but a 3/4" barrel will give you decent perfomance with typical compressor/track pump pressures which PVC can handle well.

-I'll also need advice on the various valves, hoses, and parts that I'll use.


Depends on your budget, tooling and materials available to you and how good you are at putting it all together.

-For example, I'll hook up the launcher to an air compressor or a co2 tank, depending where I am. What valve should I use?


A compressor puts out about 150 psi. An unregulated CO<sub>2</sub> tank puts out 800-900 psi, so there are a lot of fittings that would go between that and the fill valve to make it safe. A schrader valve is generally your best bet.
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Unread postAuthor: Ed » Fri Aug 03, 2012 12:14 pm

What calibre/s are you planning on, and what performance do you expect?


If I can't figure out a way to adapt a bolt action mechanism or the sleeved barrel design you showed me to work with changing barrels, then I'll stick with a 1 1/2" barrel primarily suited towards golf balls.

What calibre/s are you planning on, and what performance do you expect?


As for performance, I don't know how typical over/under pneumatic QEV guns perform, so I can't gauge what I want, in terms of "I want this thing shot X yards!". In psi, I want a cannon that can handle up to 140 psi at the least, but could still be handheld. From what I've read, 140 psi seems to be powerful for a pvc gun.

Depends on your budget, tooling and materials available to you and how good you are at putting it all together.


Budget is $100 not including the cost of the QEV. Could stretch to $150 if using metal. Materials will come from home depot/ lowe's or online. If there's a tool I'll need that I don't have, I'll borrow it from my friend, who's a contractor. He can also help me with the construction if I get stuck, so I'm not terribly worried about mods.

A compressor puts out about 150 psi. An unregulated CO2 tank puts out 800-900 psi, so there are a lot of fittings that would go between that and the fill valve to make it safe. A schrader valve is generally your best bet.


I've heard that schrader valves leak slightly, which would mean the QEV valve could unexpectedly open. Is this true, and, if it is, is there a way to 'secure' the valve?
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Unread postAuthor: Zeus » Fri Aug 03, 2012 6:03 pm

They don't leak. How often you have to refill your car tyres? However a lot of filing connectors for shraders a pretty much hopeless past a few hundred PSI. So a quick connect with a shrader adaptor would be perfect.

If you can use threaded steel, then do it, it'll handle ridiculous pressures, and dwarf any similar PVC launchers. 600PSI wouldn't be a stretch for it.

Regarding your barrel, have a look for threaded aluminium camlocks, Ths female fitting is expensive, but you can have as many male fittings you like, and they'e quite cheap. You'll only need a 3/4" set.
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Unread postAuthor: Ed » Fri Aug 03, 2012 10:28 pm

Can you provide a picture of the quick disconnect w/ the schrader adaptor?

If you can use threaded steel, then do it, it'll handle ridiculous pressures, and dwarf any similar PVC launchers. 600PSI wouldn't be a stretch for it.


Wouldn't it also be heavy? How expensive would it generally be?

Regarding your barrel, have a look for threaded aluminium camlocks, Ths female fitting is expensive, but you can have as many male fittings you like, and they'e quite cheap. You'll only need a 3/4" set.


I've seen those around, and they're a good idea for interchanging barrels, but I don't know how to adapt them to the same sleeved barrel/bolt-action breech loading mechanism, and I'm not fond of the idea of disconnecting the barrel every time to reload.
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